Some Clarity Regarding Patching Microsoft Silverlight Runtimes

As of this writing (06 May 2011), there are four production versions of Microsoft Silverlight – versions 1 through 4. Silverlight 5 is currently in beta. According to Microsoft, they will still provide security patches as they see fit for all five versions of Silverlight. However, you can no longer receive free support for Silverlight versions 1 through 3. For normal usage, versions 1 and 2 went off support on 12 October 2010. Version 3 went off support on 12 April 2011.

If you use Silverlight in production at all, you should aim to have all of those runtimes at the version 4.x level. Full details for Microsoft’s support policy for Silverlight are at the link below.